Vertical lift aircraft having an annular air foil construction can be classified into two broad areas. The first area includes those which draw air from a position above the aircraft and direct the air over an upper surface of the annular airfoil. Examples of such aircraft are found in U.S. Pat. Nos. 2,927,746, 2,978,206, 3,073,551, 4,214,720 and 4,566,699.
The second type of aircraft includes those which draw air in from a position beneath the aircraft, accelerates the air by means of a propulsion system and directs the accelerated air over the upper surfaces of the airfoil. Examples of such aircraft are found in U.S. Pat. Nos. 4,674,798 and 3,397,853.
U.S. Pat. No. 4,674,708 teaches an aircraft having an annular airfoil with planar upper and lower surfaces. Air is drawn in through a base opening and is accelerated by a turbo jet engine located in a central passageway and is directed over the upper surface of the annular air foil. Due to the configuration of the air foil, air does not circulate around the upper and lower surfaces of the airfoil but instead is flung off the peripheral edge of the airfoil. This patent does not teach an airfoil configuration which allows air to circulate around the airfoil and which directs a portion of air circulating around the airfoil to below the aircraft to provide additional thrust.
U.S. Pat. No. 3,397,853 discloses an aircraft having an annular body and a central passageway. A propulsion unit is located within the central passageway. A deflector is located above the passageway to deflect accelerated air over the annular body. A cup or dish shaped member is located below the central passageway and extends sufficiently past the widest portion of the annular body to capture all the air flowing over the annular body.
The configuration of the dish shaped member does not allow a portion of the circulated air to be split off from the main stream to be diverted to beneath the aircraft to provide additional thrust. There is no teaching in this patent that the dish shaped member can be used to split circulating air flow.